I'm familiar with the surf representation+color by volume method, in fact that is the one I've been employing.
However the added 1.4 A radius from the solvent accessible surface starting from the molecular surface does present changes in the elec trostatic profile, being them less intense (with more pronounced white/neutral regions).
If you take PyMol's APBS plugin as an example, under the Visualization tab you can check/uncheck the solvent acc. surf. box and see the difference (as briefly described here http://www.pymolwiki.org/index.php/Protein_contact_potential) .
In VMD I can simulate the same color pattern by setting the representation to VDW with added 1.4 radius, or more or less with surf rep. and a larger probe radius.
So Josh's suggestion of writing a script to color the SASA points by volume is what could come closer to what I need, however I was hopping there was a more direct way to do so with the surface/MSMS representation.

> I'm not sure if this is what you want, but it sounds like you are
> trying to just color an approximation of the protein boundary by
> what is loaded into the volumetric data. What I do is just use the
> quicksurf representation for my protein (which isn't quite SASA, but
> is close enough), and then color by volume. I believe the displayed
> points that SASA can generate are just graphics objects, so if you
> are really keen you can write a script and color them all yourself,
> but I think quicksurf + color by volume is close to what you want
> with much less fussing around.